It's far too easy to become over involved in a project, spending hours upon hours at your desk, working hard to rech the next checkpoint on your schedule. Committment to the project is admirable but slaving away hour after laborious hour, probably isn't the best way to achieve your goals. In fact it well may even be counter productive.
Over the years we have found many reasons to turn off the computer and to do something else and a small handful are listed below.

Health

By far and above the best reason to take regular breaks is your health. Not only will it help to prevent back issues, posture problems and rsi but your mental health will improve too. We all need variety in our life to keep us engaged, stimulated and engaged. Don't switch off the mac and head off to play Destiny though. DO something completely unrelated and preferably that doesn't involve a screen. The benefits to your health are huge.

Hobbies

Get a hobby. If you don't already try to find something that captures your interest and maybe will encourage you to learn a new skill. Multiple hobbies are good too. For instance I like mountain biking as it gets me out into nature (and keeps me fit) but I've also always played a few instruments and I have a few guitars around the house. That has recently led me to start something new and I'm currently building a valve amp from scratch. Hand soldering my own designed circuit, building the cabiet and everything. I'm learning lots of new skills and I'll (hopefully) have a really cool amp at the end of it.

Mixed media

You might think this is a bit of a cheat but try working with a different media. It doesn't count as actual work but will help in the long run. If you work in 3D try grabbing some pencils and draw. It's a very different way of creating and there is something that happens in the brain that is completely different to creating digitally, something even a cintiq can't replicate.

Life drawing

I recommend this to any artist, photographer or cinematographer, even if they are never going to be working with people. Not just because it can help to undertsand silhouette, form and anatomy but because it forces you to experience yoursurroundings differently, focusing the mind and eye in a way you probably wouldn't normally.

Relationships

I don't mean romantic ones, although they could be included, but just normal human interaction. I know so many digital creatives that don't really interact with people, at least not on any meaningful way. CLoseted up at their workstations they will nod and say hi as they travel to and from work but rarely make time to have quality conversations, or spend time doing things they enjoy. Not only is it just good for the soul but could potentially even open up opportunities, either for collaboration or potential client work.

It's all related

Ok, so the points above are all completely valid, either idividually or together, giving many ways to improve the quality of your life but if you really can't see the benefits to you and your friends and family think of the impact on your work too.
If you are fit and healthy, with a stimulated mind (by which I don't mean wacthing endless youtuve videos and reading blogs) and people who you regularly chat to your work will be so much better. You will be able to concentrate better making you more efficient which in turn will let you get away more (see where this is heading). You'll think in different ways and talking to others could spark an interesting idea you wouldn't have had otherwise.
Learning new skills and/or spending some time doing something you love just for the sake of it will keep you happy but still has knock on affects at your desk.
Basically what I'm saying is stop working to make the work you do do better, in almost everyway. Of course you have to pay the bills and hit deadlines but spending an afternoon here or a morning there doing something for yourself will pay back almost immediately.
On a daily basis stop every now and then and go outside, play football or join a dance class. Even sitting somewhere pleasant and reading for an hour can have a huge benefit to you and your work.

If you have a tip to help improve the working day share it in the comments below.